1. Field of the Invention
The present invention relates to an organic light emitting device such as an organic electroluminescent device and more particularly relates to an organic light emitting device using an innovative compound as an organic luminescent substance.
2. Related Art
As a thin type light emitting device, an organic electroluminescent (EL) device has extensively been investigated and a complex, aluminum tri(8-hydroxyquinoline) (Alq), having a structure in which 8-hydroxyquinoline (q) is coordination-bonded with aluminum has widely been used as an electron transporting material for an organic EL or as a main component in a doping (mixing) method. The luminescence peak wavelength in a luminescence spectrum of an Alq evaporation thin film exists near 530 nm and observed green-color luminescent light.
Further, a luminescent mixture containing a luminescent substance (a luminescent dopant) with the luminescence peak wavelength about 540 nm or longer and Alq has widely been employed to obtain luminescent color from green-color to red-color.
In the case of a full-color display being achieved by mixing primary colors, what is required is a light emitting device excellent in color purities respectively for blue-color, green-color and red-color. The color purity can be expressed in terms of chromaticity in the x-y chromaticity coordinates system of Commission International d""Eclairage (CIE). Ideal full-color display can be achieved if the obtained chromaticity for the blue-color is (x=0.14, y=0.08), for the green-color is (x=0.21, y=0.71) and for the red-color is (x=0.14, y=0.33).
A compound containing gallium and indium as a metal element belonging to group XIII as same as Al in a periodic table of elements is discussed in Appl. Phys. Lett., 1998, volume 72, Number 16, pages 1939-1941 and it is reported in the case of a gallium compound that the compound has EL peak wavelength of 502 nm and green-color emission has the chromaticity of (x=0.28, y=0.49) in the x-y chromaticity coordinates system of Commission International d""Eclairage (CIE) and in the case of an indium compound that the compound has EL peak wavelength of 545 nm and yellow green-color emission has the chromaticity of (x=0.35, y=0.56).
However, a satisfactory luminescent substance for emitting blue-color has not been found, because the color purity of such substances is either low or unstable.
An object of the present invention is to provide an organic electroluminescent device having luminescence in a wavelength range of shorter wavelength than that of green-color and more particularly, to provide an organic electroluminescent device capable of emitting blue-color with a high color purity as one of three primary colors and excellent in luminous efficiency.
The present invention according to a first aspect is an organic electroluminescent device comprising an organic luminescent substance interposed between a pair of mutually opposed electrodes, wherein the device contains at least a compound having the following general formula (I) as the organic luminescent substance: 
(in the formula, the reference character n is an integer of 3 or higher, and hydrogen bonded to any one or more of the aromatic rings may be substituted with an optional substituent).
The present invention according to a second aspect is the organic electroluminescent device as described in the first aspect, wherein the reference character n in the general formula (I) is an integer not lower than 5 and not higher than 12.
The present invention according to a third aspect is the organic electroluminescent device as described in the first or second aspects, wherein the weight per mole of the foregoing compound is 382 to 980 g/mol.
The present invention according to a fourth aspect is an organic electroluminescent device comprising an organic luminescent substance interposed between a pair of mutually opposed electrodes, wherein the device contains at least a compound having the following general formula (II) as the organic luminescent substance: 
(in the formula, the reference character n is an integer of 3 or higher, and hydrogen bonded to any one or more of the aromatic rings may be substituted with an optional substituent).
The present invention according to a fifth aspect is the organic electroluminescent device as described in the fourth aspect, wherein the reference character n in the general formula (II) is an integer not lower than 5 and not higher than 9.
The present invention according to a sixth aspect is the organic electroluminescent device as described in the fourth or fifth aspects, wherein the weight per mole of the foregoing compound is 382 to 750 g/mol.
The present invention according to a seventh aspect is an organic electroluminescent device comprising first and second layers of first and second en organic luminescent substances interposed between a pair of mutually opposed electrodes, wherein the first layer contains at least a compound having the following general formula (I) as the first organic luminescent substance 
(in the formula, the reference character n is an integer of 3 or higher and hydrogen bonded to any one or more of the aromatic rings may be substituted with an optional substituent), and the second layer contains at least a compound having the following general formula (III) as the second organic luminescent substance: 
(in the formula, the reference character m is an integer of 1 or higher, and hydrogen bonded to any one or more of the aromatic rings may be substituted with an optional substituent).
The present invention according to an eighth aspect is the organic electroluminescent device as described in the seventh aspect, wherein the compound having the general formula (I) is contained in the first layer in a proportion of 20% or higher by mole ratio.
The present invention according to a ninth aspect is the organic electroluninescent device as described in the seventh aspect, wherein the compound having the general formula (I) is contained in the first layer in a proportion of 20% or higher by weight ratio.
The present invention according to a tenth aspect is the organic electroluminescent device as described in one of the seventh to ninth aspects, wherein the first layer is formed adjacently to either one of the pair of the opposed electrodes.
The present invention according to an eleventh aspect is an organic electroluminescent device comprising an organic luminescent substance interposed between a pair of mutually opposed electrodes, wherein the device contains at least a compound having the following general formula (IV) as the organic luminescent substance: 
(in the formula, the reference characters Aa, Ab, and Az separately denote substituents with aromatic properties and may be similar or dissimilar to one another).
The present invention according to a twelfth aspect is an organic electroluminescent device comprising an organic luminescent substance interposed between a pair of mutually opposed electrodes, wherein the device contains at least a compound having the following general formula (V) as the organic luminescent substance: 
(in the formula, the reference characters Aa and Ab separately denote substituents with aromatic properties and may be similar or dissimilar to each other, and Ay denotes a substituent group having an aromatic cyclic structure).
Practical examples of the reference characters Aa, Ab, and Az in the foregoing general formula (IV) and the reference characters Aa and Ab in the foregoing general formula (V) are phenyl, naphthyl, anthryl, benzoyl, a diphenylamino group, a phenylnaphthylamino group, a dinaphthylamino group, pyridyl, oxazolyl, oxadiazolyl, phenylethynyl, arylethynyl, styryl, and the like.
In the present invention, the term xe2x80x9csubstituents with aromatic propertiesxe2x80x9d not only means the aromatic substituent groups but also includes substituent groups with aromatic cyclic structures bonded through double bonds or triple bonds. The substituent groups with aromatic cyclic structures bonded through double bonds or triple bonds are, for example, the above described phenylethynyl, arylethynyl, styryl and the like.
The present invention according to a thirteenth aspect is an organic electroluminescent device comprising an organic luminescent substance interposed between a pair of mutually opposed electrodes, wherein the device contains at least a compound having the following general formula (VI) as the organic luminescent substance: 
(in the formula, the reference character H denotes a metal, and R1, R2, R3, and R4 separately denote substituents having the following general formula (VII) and may be similar or dissimilar to one another) 
(in the formula, the reference character R5 denotes hydrogen or an optional substituent group except methyl, and R6 to R10 separately denote hydrogen or optional substituent groups).
The present invention according to a sixteenth aspect is an organic electroluminescent device comprising first and second organic luminescent substances interposed between a pair of mutually opposed electrodes, wherein the device contains at least a compound having the following general formula (VI) as the first organic luminescent substance: 
(in the formula, the reference character M denotes a metal, and R1, R2, R3, and R4 separately denote substituents having the following general formula (VII) and may be similar or dissimilar to one another) 
(in the formula, the reference characters R5 to R10 separately denote hydrogen or optional substituent groups); and a compound having the following general formula (I) as the second organic luminescent substance: 
(in the formula, the reference character n is an integer of 3 or higher, and hydrogen bonded to any one of the aromatic rings may be substituted with an optional substituent.
The present invention according to a nineteenth aspect is an organic electroluminescent device comprising an organic luminescent substance interposed between a pair of mutually opposed electrodes, wherein the device contains at least a compound having the following general formula (VI): 
(in the formula, the reference character 14 denotes a metal, and R1, R2, R3, and R4 separately denote substituents having the following general formula (VII) and may be similar or dissimilar to one another) 
(in the formula, the reference characters R5 to R10 separately denote hydrogen or optional substituent groups), and a compound having the following general formula (IV), as the organic luminescent substance: 
(in the formula, the reference characters Aa, Ab, and Az separately denote substituents with aromatic properties and may be similar or dissimilar to one another).
The present invention according to a twenty-second aspect is an organic electroluminescent device comprising an organic luminescent substance interposed between a pair of mutually opposed electrodes, wherein the device contains at least a compound having the following general formula (VI) as the organic luminescent substance: 
(in the formula, the reference character M denotes a metal, and R1, R2, R3, and R4 separately denote substituents having the following general formula (VII) and may be similar or dissimilar to one another) 
(in the formula, the reference characters R5 to R10 separately denote hydrogen or optional substituent groups); and an aromatic amine.
The present invention according to a twenty-third aspect is the organic electroluminescent device as described in the twenty-second aspect, wherein the aromatic amine is a compound having the following general formula (III): 
(in the formula, the reference character m is an integer of 1 or higher, and hydrogen bonded to any one or more of the aromatic rings may be substituted with an optional substituent).
The present invention according to a twenty-fifth aspect is the organic electroluminescent device as described in the twenty-second aspect, wherein the aromatic amine is a compound having the following general formula (VIII): 
(in the formula, the reference character m is an integer of 1 or higher).
The present invention according to a twenty-seventh aspect is the organic electroluminescent device as described in the twenty-second aspect, wherein the aromatic amine is a compound having the following general formula (IX): 
(in the formula, the reference character m is an integer of 1 or higher).
The present invention according to twenty-fourth, twenty-sixth and twenty-eighth aspects is the organic electroluminescent device, wherein the reference character m is an integer not lower than 1 and not higher than 12 in the general formulas (III), (VIII) or (IX).
The present invention according to fourteenth, Seventeenth, twentieth and twenty-ninth aspects is the organic electroluminescent device, wherein the metal element M in the general formula (VI) is sodium, potassium, rubidium, or cesium.
The present invention according to fifteenth, eighteenth, twenty-first and thirtieth aspects is the organic electroluminescent device, wherein the metal element M in the general formula (VI) is potassium.
In a luminescent substance in the present invention, the energy difference between two electron orbits; the highest occupied molecular orbit (HOMO) and the lowest unoccupied molecular orbit (LUMO); is wide and the substance therefore becomes suitable for emitting light in a wavelength range of shorter wavelength than that of green-color. Further, as compared with a conventional material, owing to the improved transportation property of electrons and/or holes and the increase of the quantum yield of luminescence, the luminous efficiency is improved.